When and how does the Emperor learn that Luke is Vader's son?

Question

We have a question asking When and how does Vader learn that Luke is his son?, but the Emperor knows too, as he says in The Empire Strikes Back:

We have a new enemy, the young rebel who destroyed the Death Star. I have no doubt this boy is the offspring of Anakin Skywalker.

The answer to the aforementioned question shows that in Disney canon comics, Vader found out that the one who destroyed the Death Star was named "Luke Skywalker" only when he sent out Boba Fett on a personal investigation, which the Emperor did not know about. I am looking for an answer that is in Disney canon and takes these comic book developments into account.

So how did the Emperor learn that Luke is Anakin's son? (And for that matter, that he was the one who destroyed the Death Star)?

Points to consider

There's been a lot of misunderstandings in the comments and such, so I want to reiterate a few points:

• Luke is not the only untrained force-sensitive in the Galaxy!!! There are loads of other people in the Galaxy who are force-sensitive. Just because Vader realized that the Force was strong with the pilot who destroyed the Death Star doesn't mean that it was automatically the spawn of Skywalker. Obi-Wan could have found any of thousands of people with latent Force ability and trained them, giving them his old apprentice's ligthsaber. Heck, Asoka was a powerful Force user who was with the Rebels; Vader had just as much evidence that it was her! So just because a powerful Force user destroyed the Death Star does not automatically point to it being Skywalker's son!
• Palpatine lied that Vader killed a pregnant Padmé, but he did not know that Obi-Wan took her to Polis Massa where Luke and Leia were born.
• I have yet to see any evidence that Palpatine has ever had the ability to sense a Force user from across the Galaxy—and in such a way that Vader, standing right next to said Force user, could not—much less identify the lineage of the Force user.
• Per the linked question, Vader found out after sending Boba Fett on a secret mission to learn Luke's name. There isn't any evidence that Palpatine knew about this secret mission, so he must have found out about it some other way than Vader did.

Answer 1

It hasn't been established how and when exactly he found out, other than it was at some point prior to his conversation with Vader in tESB. There's really not much to go on but I suspect Palpatine figured it out not long before that call.

We do know from the Vader comics that he at least pieced it together not long after Yavin and that his goal on Hoth wasn't to defeat the rebels but to extract Luke. That's why he so single-mindedly pursued the Falcon despite the heavy cost in personnel and equipment.

I would propose that this is when the Emperor noticed something fishy was going on (the "great disturbance in the force" he mentions) and when he pieced it together. Only one thing ever got Vader that fired up: family. The only family he ever had was Shmi, Padme & Kenobi and he knows they're all dead, so it must be someone new. The only possible explanation is that Padme gave birth before she died.

Note that Palpatine's speech in tESB (even the re-shot version with Ian McDiarmid) is almost dream-like and unfocused. It's as if he's in, or just come out of a deep trance. Meditating on the dark side to gain insight, which is likely where he found his answer.

It's well established that Palpatine depended on his foresight to inform his planning so it stands to reason he'd do so here too. Indeed if you examine his wording, it becomes quite apparent a lot is being said between the lines: -

Palpatine: There is a great disturbance in the Force.

Vader: I have felt it.

Palpatine: We have a new enemy. The young Rebel who destroyed the Death Star. I have no doubt this boy is the offspring of Anakin Skywalker.

Vader: How is that possible?

Since Vader already knows about Luke, the implication here is that he's calling Palpatine on his lie about his having killed Padme.

Palpatine: Search your feelings, Lord Vader. You will know it to be true.

This seems like the Emperor calling Vader right back on his playing dumb BS. He knows Vader knows and why he's running a rogue operation, chasing one tiny ship.

Palpatine: He could destroy us.

One could interpret that as the Emperor having seen a vision of the future in which Luke becomes a Jedi and defeats him, which, wouldn't you know it, he does!

Vader: He's just a boy. Obi-Wan can no longer help him.

Trying to play down the threat

Palpatine: The Force is strong with him. The son of Skywalker must not become a Jedi.

Again, concerned with possible future events.

Vader: If he could be turned, he would become a powerful ally.

Vader is almost clutching at straws here. He needs Luke alive and at his side so they can both depose Palpatine.

Palpatine: Yes... He would be a great asset. Can it be done?

This seems almost sardonic. He's not fooled for a second as he practically invented this move and sees right through Vader's plotting.

Vader: He will join us or die, master.

To add to that, Vader clearly believes the Emperor has had a vision of Luke and even says as much while trying to recruit him.

Vader: Luke, you can destroy the Emperor. He has foreseen this. It is your destiny!

Answer 2

One thing to keep in mind here: It was clear from the old trilogy already (without taking the comics into consideration) that Luke was known as Skywalker who had destroyed the death star to the empire. And vader knew already from episode 4 that someone strong in the force was responsible for destroying the death star.

With how things had went and knowing a jedi master was near the site where Padme seemingly died (and Vader almost) it can be reasoned that Palpatine just put 2 and 2 together faster than Vader did. And when he felt the increase in power...the emergence of someone who is becoming a Jedi knight he was sure they were played for.

With the comics it is currently not known if there is any other reason as they are still ongoing but so far nothing indicated that Palpatine got to know about Skywalker by any other source.

Answer 3

Rather than a straight answer, I want to question your assertion in your clarifications that Palpetine did not know that Padme survived to give birth. At the very least, he knows that Padme's dead body was not found on Mustafar, meaning that Obi-Wan took her with him. He also most likely knows that she was very pregnant with Anakin's child, and while Darth Vader seems to assume that the child she was carrying did not survive the birth either, Palpetine likely draws the opposite conclusion, so while he did not know the details, he could be fairly certain that Anakin's child survived. Indeed, there is a good chance that he is watching for Anakin's child to some day rise. So it is not far fetched to assume that, upon hearing that Obi-Wan had come out of hiding, Palpetine would expect him to bring Anakin's child with him. Indeed, I believe that Palpetine was waiting for this to happen.

Palpetine was a long-game schemer. He likely knew or at least expected that Obi-Wan had taken Anakin's child to Tatooine, but rather than dealing with a potential threat, he allowed the young Skywalker to grow up, in the hopes of one day bringing him to the dark side. He very nearly succeeds in either bringing Luke in, or strengthening Vader's darkness. In fact, one could argue that the source of Palpetine's downfall is Leia, whom the Emperor did not seem to know about or plan for. It was Vader's threat to her that inspires Luke to defeat his father, and likely Vader was thinking not only of Luke suffering before his eyes, but also what his master could do to his daughter, when he rallied the strength to destroy the Emperor.

Answer 4

This is just a theory as to how he learns, so it's just speculation.

The emperor has shown to be skilled in seeing the future using the force. For example, he foresaw that Luke will come to Vader in episode VI. When Luke saw the future in episode V he saw a city in the clouds, something he never saw before, so he learned something new. Therefore it is not unreasonable to assume that he learned about Luke being Vader's son by trying to sense the future.

Answer 5

Possibly the storm-troopers that killed Luke's Aunt and Uncle took DNA from the house and found a family match with Vader. This however is admittedly an answer that asks more questions than it answers.

Answer 6

In Star Wars: A New Hope, when Luke is attempting to destroy the Death Star, he deactivates his targeting computer because at that moment he could feel the Force flowing through him and around him.

"...the Force is what gives a Jedi his power. It's an energy field created by all living things. It surrounds us and penetrates us; it binds the galaxy together."
_{―Obi-Wan Kenobi}

If the Force connects every living thing in the galaxy together there is almost no way that a very wise and experienced force user, such as The Emperor, would not be able to sense the presence of the Force being tapped into. Especially in such a vicinity as the exact space station he is posted.

Also, keep in mind that the Jedi are "extinct" at the moment. However, The Emperor is aware of the children that Anakin Skywalker is father to. With Obi-Wan dead, and Yoda presumed dead, the only potential Force user that would stand against the Galactic Empire would be one of the children of one of the most powerful Force users in the galaxy at the time- Anakin Skywalker AKA Darth Vader.

Answer 7

After watching the entire series more than once, I think it would be a safe bet that the Emperor knew of Skywalker's existence at the end of Revenge of the Sith.

Remember, Anakin Skywalker spent a lot of time with Palpatine. No doubt they would have had a conversation about his wife being pregnant at some point. Obi-Wan, Yoda, and Organa all agreed on the danger of the new Empire. No doubt at least Yoda would have known that Luke would eventually be a potential threat to the Emperor-thus sending him to live with his closest possible relatives.

In The Empire Strikes Back, we see Vader and Palpatine conversing about the offspring of Skywalker, which would only be 1 person, Luke. After blowing up the Death Star and the ensuing celebration, it would be logical to conclude that he would have remembered "Skywalker" had offspring, and that this Son of Skywalker would have been responsible. He recognized the threat immediately, knowing that Luke would be dangerous due to who is father was. After all, Palpatine is a master of the dark side, he could have just searched Vader's feelings.